Method of anchoring a bundle of reinforcing wires or strands for pre-stressed concrete, and anchoring construction

ABSTRACT

Anchorage of a bundle of reinforcing wires or strands for prestressed concrete in a tapered throughbore of an anchoring block, in which said wires or strands are clamped relatively to the wall of the throughbore by driving a wedge into said bore, whereafter as the bundle is subsequently caused to assume its final prestressed condition, the bundle pulls itself with the wedge into a more tightly wedged position in the bore, and wherein, before the wedge is driven in sliding pieces are interposed between the wires or strands and the wall of the throughbore, said sliding pieces being formed so that as the bundle pulls itself tightly into the bore, said sliding pieces exclusively move relatively to said wall, without moving relatively to the wires or strands. The sliding pieces preferably have a prismatic shape.

nited States Patent 1 1 51 erbschleb et al. I

METHOD OF ANCHORING A BUNDLE OF REINFORCING WIRES OR STRANDS FOR PRE-STRESSED CONCRETE, AND ANCHORING CONSTRUCTION lnventors: Jan Frederik Herbschleb,

Leidschendam; Albert Komijn, Rijswijk Z.-l-l.; Hans Egbert Westenberg, The Hague, all of Netherlands 1.13.1.8. Nederland N.V., Rijswijk, Netherlands Dec. 21, 1971 Assignee:

Filed:

Appl. 196.; 210,329

Foreign Application Priority Data Dec. 24, 1970 Netherlands 7018796 us. c1. 24/122.6, 52/223 L 161. c1. F16g 11/00 Field 6: Search 52/223 13,230; 24/1223,

24/l22.6, 263 D1), 126 K, 126 L, 126 c, 136 K, 136 1., 136 B,'126.R,'136 R References Cited UNITED STATES PATENTS l/l92l Kearney..... 24/136R 10/1927 Haworth 24/126 K 2/1959 .Anderson... 24/263 DD 7/1962 Anderson 24/122.6

1111*" 3,822,442 1451 July 9, 1974 Howlett 52/223 L Italy 24/126 R Primary ExaminerDonald A. Griffin Attorney, Agent, .or Firm-'Weingarten, Maxham & Schurgin 1 57 ABSTRACT Anchorage of a bundle of reinforcing Wires or strands for pre-stressed concrete in a tapered throughbore of an anchoring block, in which said wires or strands are clamped relatively to the wall of the throughbore by driving a wedge into said bore, whereafter as the bundle is subsequently caused to assume its final prestressed Condition, the bundle pulls itself with the I wedge into a more tightly-wedged position in the bore,

and wherein, before the wedge is driven in sliding pieces are interposed between the wires or strands and the wall of the'throughbore, said sliding pieces being formedso that as the bundle pulls itself tightly into the bore, said sliding pieces exclusively move relatively to said wall, without moving relatively to the wires or strands. The sliding 'pieces preferably have a prismatic shape.

6- Claims, 6 Drawing Figures PATENIEDJIIL 9 1 3322.442

SHEET 2 0f 2 FIGS 9 v V a w m FIGS PRE-STRESSED CONCRETE, AND ANCHORING CONSTRUCTION the wall of the throughbore in the anchoring block during the last'phase of this anchoring process. As a result of local high stress concentrations in the reinforcing wiresor strands while they where laterally clamped, the wires often broke at a tensile force considerably lower than corresponded with their calculated tensile strength. It has been found that in these cases breakage was initiated on the side of the wire or strand which is in contact with the wall of the throughbore in the anchoring block. An important role in this connection is played by plastic deformation of the reinforcing wires or strands and the local high stress concentrations referred to, in particular concentrations of shearing stresses resulting from sliding along the throughbore I wall in connection with the linear contact between the wires and said wall-or point contact in the case of stranded reinforcing material.

It is an object of the present invention to provide a method of the kind referred toin the opening paragraph of this specificatiomwhich overcomes the above and similar disadvantages of methods applied hitherto.

To this effect such a method according to the invention is characterized in that beforethewedge is driven in sliding pieces are interposed between the wires or strands and the wall of the throughbore, said sliding pieces being formed so that as the bundle pulls itself tightly into the bore said sliding pieces move exclusively relatively to said wall without moving relatively to the wires or strands. It is accordingly ensured that there is less friction between the sliding pieces and the wall of the throughbore than there is between the sliding pieces and the wires or strands of the bundle.

The'invention further relates to an anchoring construction of a bundle of reinforcing wires or strands for pre-stressed concrete, anchored in a tapered throughbore of an anchoring block by the above method.

Preferably, according to the invention, the sliding pieces of such an anchoring constructionhave a generally prismatic configuration. T In a further elaboration of the invention the sliding pieces used in such an anchoring construction have on their side facing the wires or strands a surface profiled by scratching, grooves, teeth, ridges or like provisions.

In another embodiment of the invention, instead of such provisions in the material of the sliding pieces proper, the sliding pieces may have a surface on the side facing the wires or strands, which has been rougherred by friction increasing granules applied to the material of the sliding pieces.

her consisting of one piece of material. Some embodiments of the invention will be described with reference to the accompanying diagrammatic Another method of ensuring that in the last anchoring phase the reinforcing elements of the bundle do not move relatively to the sliding pieces, but the bundle does move relatively to the wall of the throughbore, in particular in the case of non-prismatic reinforcing rods or reinforcing strands, consists in using sliding pieces of a material softer than the high-grade steel of the wires or strands of the bundle, so that as the wires or strands become wedged they bed into the sliding pieces while deforming the surface of the latter.

Furthermore, according to the invention, the surfaces in contact with the reinforcing elements may be provided with berths for receiving said elements, which makes for convenience in applying the sliding pieces and holding them in place.

throughbore as one whole. This facilitates the assembly 7 of the anchoring construction. s

Also, according to the invention; at least a number of the sliding pieces may be constituted by a conical mem- FIGS. 5 and 6 show still another embodiment.

It should first be noted that the inventionis not in-- tended to be limited by the embodiments shown, but that, rather, within the scope of the invention many variant forms are possible, in particular as regards the surface design of the sliding pieces with a view to their contact with the wires or strands, and as regards-the cross-sectional.configuration of said sliding pieces. I Furthermore, although the invention relates in particular to the applications in which, while the wedge is driven in, the bundle has already been pre-stressed, it is not limited to that particular case, but also relates to the cases in which the wedge is driven in when the bundle of wires or strands has not yet been pre-stressed, which may occur, for example, if the end of the bundle concerned has no provisions for tensioning the bundle,

'in other words, the external application of pre-stress is effected from the other end of the bundle.

Referring to the drawings, 1 designates an anchoring block, 2 a frusto-conical throughbore in said anchoring block, 3 the wall of said throughbore, constituted, for example, by a sheet metal liner, 4 a frusto-conical wedge, for-example, of steel, 5 a central hole through the wedge, and 6 the elements of an anchoring bundle,

consisting of strands or wires. v

In the embodiment of FIG. 1 and 2 a sliding piece 7 is used for each strand 6 of the reinforcing bundle, the sliding pieces having the shape of a circle segment in cross-section and 'being provided 'with a shallow, groove-shaped berth 8 complementary to a peripheral portionof the strand; In the case under consideration thesliding pieces 7 are made of a material considerably softer than the high-grade steel used for the strands 6.

When the wedge is driven in, and in particular when the bundle pulls itself into the frusto-conical throughbore, the strands bed into the contacting groove profile of the sliding pieces, so that there is no relative movement. As the bundle is pulled into throughbore 2 it moves together with sliding pieces 7 along wall 3.

In the embodiment of FIG. 3 and 4, the sliding pieces are combined into one sliding body 9, constituted by a frusto-conical shell. ln orderthat it may slide slightly inwardly into the tapered throughbore, the shell is formed with an interruption at its circumference, extending along a generatrix.

The circumferential inner surface of shell 9 is provided with berths 10 adapted to strands 6. At these points, ridges are formed in the inner wall of the frustoconical shell, which ensure that the bundle and the shell move together relatively to the wall 3 as the bundle pulls itself tightly into the bore.

In the embodiment of FIGS. 5 and 6, strips 11, slightly curved in cross-section, are used as sliding pieces for the strands 6 of the reinforcing bundle. In this case the sliding pieces have no recesses forming berths, as in the exmaples described above. On the side facing the strands 6, teeth 12 are formed on strips 11, the meaning of which will be clear from the above.

Reference numeral 13 designates a ring, shown diasimilar to the taper angle of said throughbore;

the wires of said bundle passing through said throughbore, each wire being engaged between said wedge and one of said sliding members, said wires being individually spaced around the periphery of said wedge;

a portion of the inner surface of each of said sliding members contact the surface of one of said wires, said sliding members being provided with means to insure that there is substantially no relative motion between said wires and said sliding members when they are in engaged anchoring condition;

whereby when said wedge and said bundle of wires are moved in the direction toward the smaller end of said throughbore, said sliding members also move longitudinally with respect to said throughbore.

2. The apparatus according to claim'l wherein said bundle consists of non-prismatic wires, said sliding members being made of a material softer than the highgrade steel of said wires so that said wires embed into said sliding pieces as said wires, wedge and sliding members become tightly confined within the smaller end of said throughbore.

3. The apparatus according to claim 2 wherein a portion of the inner surface of each said sliding member is complementary with a portion of the perphery of one of said wires to thereby partially surround a portion of said wire.

4. The apparatus according to claim 1 wherein said sliding members are of substantially prismatic shape.

5. The apparatus according to claim 1 wherein said throughbore.

6. The apparatus according to claim 1 wherein said friction inducing means on said sliding members includes friction increasing granules or like particles applied to the inner surface of said sliding members. 

1. Apparatus for anchoring a bundle of reinforcing wires for prestressed concrete, said apparatus comprising: an anchoring block having a relatively smooth tapered throughbore; a plurality of arcuate sliding members, each having an outer smooth surface conforming to the inner surface of said throughbore and having a substantially uniform thickness in the longitudinal direction; and a frusto-conical wedge having an external taper angle similar to the taper angle of said throughbore; the wires of said bundle passing through said throughbore, each wire being engaged between said wedge and one of said sliding members, said wires being individually spaced around the periphery of said wedge; a portion of the inner surface of each of said sliding members contact the surface of one of said wires, said sliding members being provided with means to insure that there is substantially no relative motion between said wires and said sliding members when they are in engaged anchoring condition; whereby when said wedge and said bundle of wires are moved in the direction toward the smaller end of said throughbore, said sliding members also move longitudinally with respect to said throughbore.
 2. The apparatus according to claim 1 wherein said bundle consists of non-prismatic wires, said sliding members being made of a material softer than the high-grade steel of said wires so that said wires embed into said sliding pieces as said wires, wedge and sliding members become tightly confined within the smaller end of said throughbore.
 3. The apparatus according to claim 2 wherein a portion of the inner surface of each said sliding member is complementary with a portion of the perphery of one of said wires to thereby partially surround a portion of said wire.
 4. The apparatus according to claim 1 wherein said sliding members are of substantially prismatic shape.
 5. The apparatus according to claim 1 wherein said sliding members are interconnected by at least one ring extending therebetween adjacent to the wall of said throughbore.
 6. The apparatus according to claim 1 Wherein said friction inducing means on said sliding members includes friction increasing granules or like particles applied to the inner surface of said sliding members. 